<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <script>
        var a = prompt('输入你的分数')
        if (a >= 90 ) {
            alert('A')
        }else if (a >= 80) {
            alert('B')
        }else if (a >= 70) {
            alert('C')
        }else if (a >= 60) {
            alert('D')
        }else  {
            alert('E')
        }
    </script>
</body>
</html>